RESUMO
Activation of protein kinases after cocaine administration controls psychomotor behaviours by interacting with metabotropic receptors in the brain. This study identified how c-Jun N-terminal kinase (JNK) interacts with metabotropic glutamate receptor 5 (mGluR5) in vitro and in the caudate and putamen (CPu). The potential role of this interaction in the regulation of psychomotor behaviour was also evaluated after administration of cocaine. Active JNK phosphorylates a threonine residue at position 1055 in the carboxyl terminus (CT) of mGluR5 in vitro. The binding of active JNK to the D-motif within CT2 is necessary for that phosphorylation. Interaction of phosphorylated JNK and mGluR5 occurs in the CPu. Unilateral interference of the interaction decreases the repeated cocaine-induced increases in locomotor activity and conditioned place preference. These findings suggest that activation of JNK has the capability to interact with mGluR5 in the CPu. Phosphorylation of mGluR5 following the JNK-mGluR5 interaction may be responsible for the potentiation of behavioural sensitisation and cocaine-wanting behaviour in response to cocaine administration.
Assuntos
Cocaína , Receptor de Glutamato Metabotrópico 5 , Encéfalo/metabolismo , Cocaína/metabolismo , Cocaína/farmacologia , Fosforilação , Putamen/metabolismo , Receptor de Glutamato Metabotrópico 5/metabolismoRESUMO
Major depressive disorder is a chronic psychiatric disease with a high prevalence. Brain mechanisms for depression at cellular and molecular levels are far from clear. Increasing evidence from clinical and preclinical studies reveals critical roles of the non-receptor tyrosine kinase (nRTK) superfamily in the pathophysiology, symptomatology, and therapy of depression. To date, several nRTK members from three nRTK subfamilies, i.e., the Src family kinase (SFK), the Janus tyrosine kinase (JAK) and the focal adhesion kinase (FAK) subfamilies, may connect to the intracellular, intranuclear, and synaptic signaling network linking chronic stress to depression- and anxiety-like behavior. These SFK/JAK/FAK nRTKs are abundantly expressed in the prefrontal cortex and hippocampus, two core limbic regions implicated in depression, and are enriched at synaptic sites. In various acute or chronic animal models of depression, the nRTKs were significantly altered (up- or downregulated) in their phosphorylation, expression, subcellular/subsynaptic distribution, and/or function. Stress that precipitates depressive behavior also influenced the interaction of nRTKs with other signaling molecules and downstream substrates, including ionotropic and metabotropic glutamate receptors. The commonly-used antidepressants showed the ability to alter nRTK activity. In sum, the limbic SFK/JAK/FAK nRTKs are sensitive to stress and undergo drastic adaptations in response to chronic depression. These long-lasting adaptations contribute to the remodeling of signaling network or synaptic plasticity critical for the vulnerability to depression and the therapeutic efficacy of antidepressants.
Assuntos
Depressão/tratamento farmacológico , Depressão/metabolismo , Proteínas Tirosina Quinases/efeitos dos fármacos , Proteínas Tirosina Quinases/metabolismo , AnimaisRESUMO
Group I metabotropic glutamate (mGlu) receptors (mGlu1/5 subtypes) are G protein-coupled receptors and are broadly expressed in the mammalian brain. These receptors play key roles in the modulation of normal glutamatergic transmission and synaptic plasticity, and abnormal mGlu1/5 signaling is linked to the pathogenesis and symptomatology of various mental and neurological disorders. Group I mGlu receptors are noticeably regulated via a mechanism involving dynamic protein-protein interactions. Several synaptic protein kinases were recently found to directly bind to the intracellular domains of mGlu1/5 receptors and phosphorylate the receptors at distinct amino acid residues. A variety of scaffolding and adaptor proteins also interact with mGlu1/5. Constitutive or activity-dependent interactions between mGlu1/5 and their interacting partners modulate trafficking, anchoring, and expression of the receptors. The mGlu1/5-associated proteins also finetune the efficacy of mGlu1/5 postreceptor signaling and mGlu1/5-mediated synaptic plasticity. This review analyzes the data from recent studies and provides an update on the biochemical and physiological properties of a set of proteins or molecules that interact with and thus regulate mGlu1/5 receptors.
Assuntos
Proteínas de Transporte/metabolismo , Receptores de Glutamato Metabotrópico/metabolismo , Animais , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Ácido Glutâmico/metabolismo , Humanos , Sistema de Sinalização das MAP Quinases , Fosforilação , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Isoformas de Proteínas , Proteína Quinase C/metabolismo , Transporte Proteico , Receptores de Glutamato Metabotrópico/química , Receptores de Glutamato Metabotrópico/genética , Transdução de Sinais , Relação Estrutura-AtividadeRESUMO
Acid-sensing ion channels (ASICs) are mainly proton-gated cation channels that are activated by pH drops and nonproton ligands. They are part of the degenerin/epithelial sodium channel superfamily due to their sodium permeability. Predominantly expressed in the central nervous system, ASICs are involved in synaptic plasticity, learning/memory, and fear conditioning. These channels have also been implicated in multiple disease conditions, including ischemic brain injury, multiple sclerosis, Alzheimer's disease, and drug addiction. Recent research has illustrated the involvement of ASICs in mechanosensation. Mechanosensation is a form of signal transduction in which mechanical forces are converted into neuronal signals. Specific mechanosensitive functions have been elucidated in functional ASIC1a, ASIC1b, ASIC2a, and ASIC3. The implications of mechanosensation in ASICs indicate their subsequent involvement in functions such as maintaining blood pressure, modulating the gastrointestinal function, and bladder micturition, and contributing to nociception. The underlying mechanism of ASIC mechanosensation is the tether-gate model, which uses a gating-spring mechanism to activate ASIC responses. Further understanding of the mechanism of ASICs will help in treatments for ASIC-related pathologies. Along with the well-known chemosensitive functions of ASICs, emerging evidence has revealed that mechanosensitive functions of ASICs are important for maintaining homeostasis and contribute to various disease conditions.
Assuntos
Canais Iônicos Sensíveis a Ácido/genética , Canais de Sódio Degenerina/genética , Mecanotransdução Celular/genética , Neurônios/metabolismo , Canais Iônicos Sensíveis a Ácido/metabolismo , Animais , Canais de Sódio Degenerina/metabolismo , Humanos , Esclerose Múltipla/genética , Esclerose Múltipla/patologia , Plasticidade Neuronal , Sódio/metabolismoRESUMO
Major depressive disorder is a common form of mental illness. Many brain regions are implicated in the pathophysiology and symptomatology of depression. Among key brain areas is the striatum that controls reward and mood and is involved in the development of core depression-like behavior in animal models of depression. While molecular mechanisms in this region underlying depression-related behavior are poorly understood, the glutamatergic input to the striatum is believed to play a role. In this study, we investigated changes in metabotropic glutamate (mGlu) receptor expression and signaling in the striatum of adult rats in response to prolonged (10-12 weeks) social isolation, a pre-validated animal paradigm modeling depression in adulthood. We found that mGlu5 receptor protein levels in the striatum were increased in rats that showed typical depression- and anxiety-like behavior after chronic social isolation. This increase in mGlu5 receptor expression was seen in both subdivisions of the striatum, the nucleus accumbens and caudate putamen. At subcellular and subsynaptic levels, mGlu5 receptor expression was elevated in surface membranes at synaptic sites. In striatal neurons, the mGlu5-associated phosphoinositide signaling pathway was augmented in its efficacy after prolonged social isolation. These data indicate that the mGlu5 receptor is a sensitive substrate of depression. Adulthood social isolation leads to the up-regulation of mGlu5 receptor expression and function in striatal neurons.
Assuntos
Corpo Estriado/metabolismo , Depressão/metabolismo , Receptor de Glutamato Metabotrópico 5/metabolismo , Animais , Modelos Animais de Doenças , Masculino , Ratos , Ratos Wistar , Isolamento SocialRESUMO
Acetylcholine (ACh) is a key transmitter in the mesocorticolimbic circuit. By interacting with muscarinic ACh receptors (mAChR) enriched in the circuit, ACh actively regulates various neuronal and synaptic activities. The extracellular signal-regulated kinase (ERK) is one of members of the mitogen-activated protein kinase family and is subject to the regulation by dopamine receptors, although the regulation of ERKs by limbic mAChRs is poorly understood. In this study, we investigated the role of mAChRs in the regulation of ERK phosphorylation (activation) in the mesocorticolimbic system of adult rat brains in vivo. We targeted a sub-pool of ERKs at synaptic sites. We found that a systemic injection of the mAChR antagonist scopolamine increased phosphorylation of synaptic ERKs in the striatum (caudate putamen and nucleus accumbens) and medial prefrontal cortex (mPFC). Increases in ERK phosphorylation in both forebrain regions were rapid and transient. Notably, pretreatment with a dopamine D1 receptor (D1R) antagonist SCH23390 blocked the scopolamine-stimulated ERK phosphorylation in these brain regions, while a dopamine D2 receptor antagonist eticlopride did not. Scopolamine and SCH23390 did not change the amount of total ERK proteins. These results demonstrate that mAChRs inhibit synaptic ERK phosphorylation in striatal and mPFC neurons under normal conditions. Blockade of this inhibitory mAChR tone leads to the upregulation of ERK phosphorylation likely through a mechanism involving the level of D1R activity.
Assuntos
MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Antagonistas Muscarínicos/farmacologia , Prosencéfalo/metabolismo , Receptores Muscarínicos/metabolismo , Sinapses/metabolismo , Transmissão Sináptica/fisiologia , Animais , Benzazepinas/farmacologia , MAP Quinases Reguladas por Sinal Extracelular/antagonistas & inibidores , Masculino , Fosforilação/efeitos dos fármacos , Fosforilação/fisiologia , Prosencéfalo/efeitos dos fármacos , Ratos , Ratos Wistar , Sinapses/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacosRESUMO
Several non-receptor tyrosine kinase (nRTK) members are expressed in neurons of mammalian brains. Among these neuron-enriched nRTKs, two Src family kinase members (Src and Fyn) are particularly abundant at synaptic sites and have been most extensively studied for their roles in the regulation of synaptic activity and plasticity. Increasing evidence shows that the synaptic subpool of nRTKs interacts with a number of local substrates, including glutamate receptors (both ionotropic and metabotropic glutamate receptors), postsynaptic scaffold proteins, presynaptic proteins, and synapse-enriched enzymes. By phosphorylating specific tyrosine residues in the intracellular domains of these synaptic proteins either constitutively or in an activity-dependent manner, nRTKs regulate these substrates in trafficking, surface expression, and function. Given the high sensitivity of nRTKs to changing synaptic input, nRTKs are considered to act as a critical regulator in the determination of the strength and efficacy of synaptic transmission.
Assuntos
Proteínas Tirosina Quinases/fisiologia , Sinapses/fisiologia , Quinases da Família src/fisiologia , Animais , Humanos , Plasticidade Neuronal , Fosforilação , Transmissão SinápticaRESUMO
Fyn, a major Src family kinase (SFK) member that is densely expressed in striatal neurons, is actively involved in the regulation of cellular and synaptic activities in local neurons. This SFK member is likely regulated by dopamine signaling through a receptor mechanism involving dopamine D2 receptors (D2Rs). This study characterizes the D2R-dependent regulation of Fyn in the rat striatum in vivo. Moreover, we explore whether D2Rs regulate metabotropic glutamate receptor 5 (mGluR5) in its tyrosine phosphorylation and whether the D2R-SFK pathway modulates trafficking of mGluR5. We found that blockade of D2Rs by systemic administration of a D2R antagonist, eticlopride, substantially increased SFK phosphorylation in the striatum. This increase was a transient and reversible event. The eticlopride-induced SFK phosphorylation occurred predominantly in immunopurified Fyn but not in another SFK member, Src. Eticlopride also elevated tyrosine phosphorylation of mGluR5. In parallel, eticlopride enhanced synaptic delivery of active Fyn and mGluR5. Pretreatment with an SFK inhibitor blocked the eticlopride-induced tyrosine phosphorylation and synaptic trafficking of mGluR5. These results indicate that D2Rs inhibit SFK (mainly Fyn) phosphorylation in the striatum. D2Rs also inhibit tyrosine phosphorylation and synaptic recruitment of mGluR5 through a signaling mechanism likely involving Fyn.
Assuntos
Corpo Estriado/metabolismo , Proteínas Proto-Oncogênicas c-fyn/metabolismo , Receptor de Glutamato Metabotrópico 5/metabolismo , Receptores de Dopamina D2/metabolismo , Animais , Western Blotting , Imunoprecipitação , Masculino , Fosforilação , Ratos , Ratos WistarRESUMO
Increasing evidence supports the critical role of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors in psychostimulant action. These receptors are regulated via a phosphorylation-dependent mechanism in their trafficking, distribution, and function. The hippocampus is a brain structure important for learning and memory and is emerging as a critical site for processing psychostimulant effects. To determine whether the hippocampal pool of AMPA receptors is regulated by stimulants, we investigated and characterized the impact of amphetamine (AMPH) on phosphorylation of AMPA receptors in the adult rat hippocampus in vivo. We found that AMPH markedly increased phosphorylation of AMPA receptor GluA1 subunits at serine 845 (S845) in the hippocampus. The effect of AMPH was dose dependent. A single dose of AMPH induced a rapid and transient increase in S845 phosphorylation. Among different hippocampal subfields, AMPH primarily elevated S845 phosphorylation in the Cornu Ammonis area 1 and dentate gyrus. In contrast to S845, serine 831 phosphorylation of GluA1 and serine 880 phosphorylation of GluA2 were not altered by AMPH. In addition, surface expression of hippocampal GluA1 was up-regulated, while the amount of intracellular GluA1 fraction was concurrently reduced in response to AMPH. GluA2 protein levels in either the surface or intracellular pool were insensitive to AMPH. These data demonstrate that the AMPA receptor in the hippocampus is sensitive to dopamine stimulation. Acute AMPH administration induces dose-, time-, site-, and subunit-dependent phosphorylation of AMPA receptors and facilitates surface trafficking of GluA1 AMPA receptors in hippocampal neurons in vivo. Acute injection of amphetamine increased phosphorylation of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 subunits at a protein kinase A (PKA)-sensitive site (S845) in the rat hippocampus. This increase was dose- and time-dependent and correlated with an increase in surface GluA1 expression. Thus, amphetamine can upregulate GluA1 phosphorylation and surface trafficking of GluA1 in hippocampal neurons in vivo.
Assuntos
Anfetamina/farmacologia , Estimulantes do Sistema Nervoso Central/farmacologia , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Receptores de AMPA/metabolismo , Animais , Western Blotting , Masculino , Fosforilação/efeitos dos fármacos , Ratos , Ratos Wistar , Receptores de AMPA/efeitos dos fármacosRESUMO
Dopamine and acetylcholine are two principal transmitters in the striatum and are usually balanced to modulate local neural activity and to maintain striatal homeostasis. This study investigates the role of dopamine and muscarinic acetylcholine receptors in the regulation of a central signaling protein, i.e., the mitogen-activated protein kinase (MAPK). We focus on the synaptic pool of MAPKs because of the fact that these kinases reside in peripheral synaptic structures in addition to their somatic locations. We show that a systemic injection of dopamine D1 receptor (D1R) agonist SKF81297 enhances phosphorylation of extracellular signal-regulated kinases (ERKs), a prototypic subclass of MAPKs, in the adult rat striatum. Similar results were observed in another dopamine-responsive region, the medial prefrontal cortex (mPFC). The dopamine D2 receptor agonist quinpirole had no such effects. Pretreatment with a positive allosteric modulator (PAM) of muscarinic acetylcholine M4 receptors (M4Rs), VU0152100, attenuated the D1R agonist-stimulated ERK phosphorylation in the two regions, whereas the PAM itself did not alter basal ERK phosphorylation. All drug treatments had no effect on phosphorylation of c-Jun N-terminal kinases (JNKs), another MAPK subclass, in the striatum and mPFC. These results demonstrate that dopamine and acetylcholine are integrated to control synaptic ERK but not JNK activation in striatal and mPFC neurons in vivo. Activation of M4Rs exerts an inhibitory effect on the D1R-mediated upregulation of synaptic ERK phosphorylation.
Assuntos
Corpo Estriado/metabolismo , Dopamina/metabolismo , MAP Quinase Quinase 2/metabolismo , Córtex Pré-Frontal/metabolismo , Receptores Muscarínicos/metabolismo , Sinapses/metabolismo , Animais , Colinérgicos/farmacologia , Corpo Estriado/efeitos dos fármacos , Dopaminérgicos/farmacologia , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Masculino , Fosforilação/efeitos dos fármacos , Córtex Pré-Frontal/efeitos dos fármacos , Ratos , Ratos Wistar , Sinapses/efeitos dos fármacosRESUMO
The metabotropic glutamate receptor 1 (mGluR1) is a Gα(q)-protein-coupled receptor and is distributed in broad regions of the mammalian brain. As a key element in excitatory synaptic transmission, the receptor regulates a wide range of cellular and synaptic activities. In addition to regulating its targets, the receptor itself is believed to be actively regulated by intracellular signals, although underlying mechanisms are essentially unknown. Here we found that a synapse-enriched protein kinase, Ca²âº/calmodulin-dependent protein kinase IIα (CaMKIIα), directly binds to the intracellular C terminus (CT) of mGluR1a. This binding is augmented by Ca²âº in vitro. The direct interaction promotes CaMKIIα to phosphorylate mGluR1a at a specific threonine site (T871). In rat striatal neurons, the mGluR1 agonist triggers the receptor-associated phosphoinositide signaling pathway to induce Ca²âº-dependent recruitment of CaMKIIα to mGluR1a-CT. This enables the kinase to inhibit the response of the receptor to subsequent agonist exposure. Our data identify an agonist-induced and Ca²âº-dependent protein-protein interaction between a synaptic kinase and mGluR1, which constitutes a feedback loop facilitating desensitization of mGluR1a.
Assuntos
Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/fisiologia , Retroalimentação Fisiológica/fisiologia , Receptores de Glutamato Metabotrópico/metabolismo , Sequência de Aminoácidos , Animais , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Corpo Estriado/enzimologia , Corpo Estriado/metabolismo , Corpo Estriado/fisiologia , Masculino , Dados de Sequência Molecular , Técnicas de Cultura de Órgãos , Fosforilação/fisiologia , Ligação Proteica/fisiologia , Ratos , Ratos WistarRESUMO
Muscarinic acetylcholine receptors (mAChRs) are widely expressed in the mammalian brain and are essential for neuronal functions. These receptors are believed to be actively regulated by intracellular signals, although the underlying mechanisms are largely unknown. In this study, we show that Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) binds directly and selectively to one of five mAChR subtypes, M4 receptors (M4Rs), at their C-terminal regions of second intracellular loops. This binding relies on Ca(2+) activation of the kinase and leads to the phosphorylation of M4Rs at a specific threonine site (Thr145). Complementary in vivo studies in rat striatal neurons enriched with M4Rs confirm that rising Ca(2+) recruits CaMKIIalpha to M4Rs to potentiate receptor signalling, which controls behavioural sensitivity to dopamine stimulation in an activity-dependent manner. Our data identify a new model of protein-protein interactions. In a Ca(2+)-sensitive manner, CaMKIIalpha regulates M4R efficacy and controls the acetylcholine-dopamine balance in the basal ganglia and also the dynamics of movement.
Assuntos
Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Domínios e Motivos de Interação entre Proteínas , Mapeamento de Interação de Proteínas , Receptor Muscarínico M4/metabolismo , Animais , Cálcio/metabolismo , Cocaína/farmacologia , Corpo Estriado/fisiologia , Inibidores da Captação de Dopamina/farmacologia , Locomoção/efeitos dos fármacos , Neurônios/fisiologia , Fosforilação , Ligação Proteica , RatosRESUMO
Ca²âº/calmodulin-dependent protein kinase II (CaMKII) is the most abundant kinase within excitatory synapses in the mammalian brain. It interacts with and phosphorylates a large number of synaptic proteins, including major ionotropic glutamate receptors (iGluRs) and group I metabotropic glutamate receptors (mGluRs), to constitutively and/or activity-dependently regulate trafficking, subsynaptic localization, and function of the receptors. Among iGluRs, the N-methyl-D-aspartate receptor (NMDAR) is a direct target of CaMKII. By directly binding to an intracellular C-terminal (CT) region of NMDAR GluN2B subunits, CaMKII phosphorylates a serine residue (S1303) in the GluN2B CT. CaMKII also phosphorylates a serine site (S831) in the CT of α-amino-3-hydroxy-5- methylisoxazole-4-propionic acid receptors. This phosphorylation enhances channel conductance and is critical for synaptic plasticity. In addition to iGluRs, CaMKII binds to the proximal CT region of mGluR1a, which enables the kinase to phosphorylate threonine 871. Agonist stimulation of mGluR1a triggers a CaMKII-mediated negative feedback to facilitate endocytosis and desensitization of the receptor. CaMKII also binds to the mGluR5 CT. This binding seems to anchor and accumulate inactive CaMKII at synaptic sites. Active CaMKII dissociates from mGluR5 and may then bind to adjacent GluN2B to mediate the mGluR5-NMDAR coupling. Together, glutamate receptors serve as direct substrates of CaMKII. By phosphorylating these receptors, CaMKII plays a central role in controlling the number and activity of the modified receptors and determining the strength of excitatory synaptic transmission.
Assuntos
Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Plasticidade Neuronal , Fosforilação , Receptor de Glutamato Metabotrópico 5/metabolismo , Receptores de Glutamato Metabotrópico/metabolismo , Serina/metabolismo , Sinapses , Transmissão SinápticaRESUMO
The commonly used general anesthetic propofol can enhance the γ-aminobutyric acid-mediated inhibitory synaptic transmission and depress the glutamatergic excitatory synaptic transmission to achieve general anesthesia and other outcomes. In addition to the actions at postsynaptic sites, the modulation of presynaptic activity by propofol is thought to contribute to neurophysiological effects of the anesthetic, although potential targets of propofol within presynaptic nerve terminals are incompletely studied at present. In this study, we explored the possible linkage of propofol to synapsins, a family of neuron-specific phosphoproteins which are the most abundant proteins on presynaptic vesicles, in the adult mouse brain in vivo. We found that an intraperitoneal injection of propofol at a dose that caused loss of righting reflex increased basal levels of synapsin phosphorylation at the major representative phosphorylation sites (serine 9, serine 62/67, and serine 603) in the prefrontal cortex (PFC) of male and female mice. Propofol also elevated synapsin phosphorylation at these sites in the striatum and S9 and S62/67 phosphorylation in the hippocampus, while propofol had no effect on tyrosine hydroxylase phosphorylation in striatal nerve terminals. Total synapsin protein expression in the PFC, hippocampus, and striatum was not altered by propofol. These results reveal that synapsin could be a novel substrate of propofol in the presynaptic neurotransmitter release machinery. Propofol possesses the ability to upregulate synapsin phosphorylation in broad mouse brain regions.
Assuntos
Propofol , Sinapsinas , Feminino , Camundongos , Masculino , Animais , Sinapsinas/metabolismo , Propofol/farmacologia , Fosforilação , Terminações Pré-Sinápticas/metabolismo , Encéfalo/metabolismo , Serina/metabolismoRESUMO
Two glutamate receptors, metabotropic glutamate receptor 5 (mGluR5), and ionotropic NMDA receptors (NMDAR), functionally interact with each other to regulate excitatory synaptic transmission in the mammalian brain. In exploring molecular mechanisms underlying their interactions, we found that Ca(2+) /calmodulin-dependent protein kinase IIα (CaMKIIα) may play a central role. The synapse-enriched CaMKIIα directly binds to the proximal region of intracellular C terminal tails of mGluR5 in vitro. This binding is state-dependent: inactive CaMKIIα binds to mGluR5 at a high level whereas the active form of the kinase (following Ca(2+) /calmodulin binding and activation) loses its affinity for the receptor. Ca(2+) also promotes calmodulin to bind to mGluR5 at a region overlapping with the CaMKIIα-binding site, resulting in a competitive inhibition of CaMKIIα binding to mGluR5. In rat striatal neurons, inactive CaMKIIα constitutively binds to mGluR5. Activation of mGluR5 Ca(2+) -dependently dissociates CaMKIIα from the receptor and simultaneously promotes CaMKIIα to bind to the adjacent NMDAR GluN2B subunit, which enables CaMKIIα to phosphorylate GluN2B at a CaMKIIα-sensitive site. Together, the long intracellular C-terminal tail of mGluR5 seems to serve as a scaffolding domain to recruit and store CaMKIIα within synapses. The mGluR5-dependent Ca(2+) transients differentially regulate CaMKIIα interactions with mGluR5 and GluN2B in striatal neurons, which may contribute to cross-talk between the two receptors. We show that activation of mGluR5 with a selective agonist triggers intracellular Ca(2+) release in striatal neurons. Released Ca(2+) dissociates preformed CaMKIIα from mGluR5 and meanwhile promotes active CaMKIIα to bind to the adjacent NMDAR GluN2B subunit, which enables CaMKIIα to phosphorylate GluN2B at a CaMKIIα-sensitive site. This agonist-induced cascade seems to mediate crosstalk between mGluR5 and NMDA receptors in neurons.
Assuntos
Cálcio/metabolismo , Proteínas de Transporte/metabolismo , Neurônios/metabolismo , Receptor de Glutamato Metabotrópico 5/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Sequência de Aminoácidos , Animais , Proteínas de Ligação ao Cálcio , Calmodulina/metabolismo , Corpo Estriado/citologia , Corpo Estriado/metabolismo , Masculino , Dados de Sequência Molecular , Núcleo Accumbens/citologia , Núcleo Accumbens/metabolismo , Fosforilação/fisiologia , Ratos , Ratos Wistar , Receptor de Glutamato Metabotrópico 5/genética , Transmissão Sináptica/fisiologiaRESUMO
Metabotropic glutamate (mGlu) receptors are involved in the experience-dependent neuroplasticity in the mesolimbic reward circuit. A Gαi/o-coupled mGlu2 subtype is distributed presynaptically in the striatum. These autoreceptors may have a significant influence over striatal neurons in their intracellular signaling pathways in response to a psychostimulant. Here we explored the effect of pharmacological potentiation of mGlu2 receptors on cocaine-stimulated phosphorylation (activation) of extracellular signal-regulated kinases (ERK) in the mouse striatum in vivo. We found that an mGlu2 selective positive allosteric modulator (PAM) LY487379 after a systemic injection did not alter basal phosphorylation of ERK1/2 or c-Jun N-terminal kinases in the striatum. However, pretreatment with LY487379 blocked the ERK1/2 phosphorylation induced by cocaine in the two subdivisions of the striatum, i.e., the caudate putamen and nucleus accumbens. LY487379 also blocked the cocaine-induced phosphorylation of Elk-1, a transcription factor downstream to the ERK pathway. Additionally, LY487379 reduced locomotor behavioral responses to cocaine. These results demonstrate that the mGlu2 PAM LY487379 possesses the ability to attenuate the activation of the ERK1/2 pathway in striatal neurons and reduce locomotor activity in response to cocaine in vivo.
Assuntos
Cocaína , Receptores de Glutamato Metabotrópico , Camundongos , Animais , Receptores de Glutamato Metabotrópico/metabolismo , Cocaína/farmacologia , Fosforilação , Sistema de Sinalização das MAP Quinases , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Ácido Glutâmico/metabolismo , Corpo Estriado/metabolismo , Proteínas de Ligação ao GTP/metabolismoRESUMO
Metabotropic glutamate (mGlu) receptors are G protein-coupled receptors. Among eight mGlu subtypes (mGlu1-8), mGlu8 has drawn increasing attention. This subtype is localized to the presynaptic active zone of neurotransmitter release and is among the mGlu subtypes with high affinity for glutamate. As a Gi/o-coupled autoreceptor, mGlu8 inhibits glutamate release to maintain homeostasis of glutamatergic transmission. mGlu8 receptors are expressed in limbic brain regions and play a pivotal role in modulating motivation, emotion, cognition, and motor functions. Emerging evidence emphasizes the increasing clinical relevance of abnormal mGlu8 activity. Studies using mGlu8 selective agents and knockout mice have revealed the linkage of mGlu8 receptors to multiple neuropsychiatric and neurological disorders, including anxiety, epilepsy, Parkinson's disease, drug addiction, and chronic pain. Expression and function of mGlu8 receptors in some limbic structures undergo long-lasting adaptive changes in animal models of these disorders, which may contribute to the remodeling of glutamatergic transmission critical for the pathogenesis and symptomatology of brain illnesses. This review summarizes the current understanding of mGlu8 biology and the possible involvement of the receptor in several common psychiatric and neurological disorders.
Assuntos
Doenças do Sistema Nervoso , Doença de Parkinson , Receptores de Glutamato Metabotrópico , Animais , Camundongos , Glutamatos , HumanosRESUMO
Five muscarinic acetylcholine (mACh) receptor subtypes are divided into two classes: the M1 class (M1, M3, and M5) and the M2 class (M2 and M4). The former is coupled to Gq proteins, while the latter is coupled to Gi/o proteins. Accumulating evidence indicates that mACh receptors play a significant role in the regulation of the Src family kinase (SFK), a subfamily of non-receptor tyrosine kinases. mACh receptors exert their roles in a subtype-dependent fashion and preferentially target Src and Fyn, two members of SFKs that are expressed in the brain and enriched at synaptic sites. While the M1 receptor positively modulates SFK activity, the M4 receptor inhibits it. By modulating SFKs, mACh receptors are actively involved in the regulation of expression and function of a variety of receptors, structural proteins, and signaling molecules. In particular, the M4 receptor and the dopamine D1 receptor are coexpressed in striatonigral projection neurons of the striatum. Gi/o-coupled M4 and Gq-coupled D1 receptors antagonistically regulate SFK activity, thereby forming a dynamic balance controlling glutamate receptor activity, excitability of neurons, and synaptic plasticity. In summary, mACh receptors play a crucial role in regulating SFK activity in heterologous cells and neurons.
RESUMO
Ionotropic glutamate receptors, especially the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subtype, undergo dynamic trafficking between the surface membrane and intracellular organelles. This trafficking activity determines the efficacy and strength of excitatory synapses and is subject to modulation by changing synaptic inputs. Given the possibility that glutamate receptors in the central nervous system might be a sensitive target of anesthetic agents, this study investigated the possible impact of anesthesia on trafficking and subcellular expression of AMPA receptors in adult mouse brain neurons in vivo. We found that anesthesia induced by a systemic injection of pentobarbital did not alter total protein levels of three AMPA receptor subunits (GluR1-3) in cortical neurons. However, an anesthetic dose of pentobarbital reduced GluR1 and GluR3 proteins in the surface pool and elevated these proteins in the intracellular pool of cortical neurons. The similar redistribution of GluR1/3 was observed in mouse striatal neurons. Pentobarbital did not significantly alter GluR2 expression in the two pools. Chloral hydrate at an anesthetic dose also reduced surface GluR1/3 expression and increased intracellular levels of these proteins. The effect of pentobarbital on subcellular distribution of AMPA receptors was reversible. Altered subcellular distribution of GluR1/3 returned to normal levels after the anesthesia subsided. These data indicate that anesthesia induced by pentobarbital and chloral hydrate can alter AMPA receptor trafficking in both cortical and striatal neurons. This alteration is characterized by the concurrent loss and addition of GluR1/3 subunits in the respective surface and intracellular pools.
Assuntos
Córtex Cerebral/citologia , Hidrato de Cloral/farmacologia , Corpo Estriado/citologia , Hipnóticos e Sedativos/farmacologia , Neurônios/efeitos dos fármacos , Pentobarbital/farmacologia , Receptores de AMPA/metabolismo , Análise de Variância , Animais , Regulação da Expressão Gênica/efeitos dos fármacos , Técnicas In Vitro , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Neurônios/ultraestrutura , Transporte Proteico/efeitos dos fármacos , Reflexo/efeitos dos fármacos , Frações Subcelulares/metabolismoRESUMO
Cocaine abuse hastens the neurodegeneration often associated with advanced HIV-1 infection. The mechanisms, in part, revolve around the neuroinflammatory processes mediated by the chemokine monocyte chemotactic protein-1 (MCP-1/CCL2). Understanding factors that modulate MCP-1 and, in turn, facilitate monocyte extravasation in the brain is thus of paramount importance. We now demonstrate that cocaine induces MCP-1 in rodent microglia through translocation of the sigma receptor to the lipid raft microdomains of the plasma membrane. Sequential activation of Src, mitogen-activated protein kinases (MAPKs), and phosphatidylinositol-3' kinase (PI3K)/Akt and nuclear factor kappaB (NF-kappaB) pathways resulted in increased MCP-1 expression. Furthermore, conditioned media from cocaine-exposed microglia increased monocyte transmigration, and thus was blocked by antagonists for CCR2 or sigma receptor. These findings were corroborated by demonstrating increased monocyte transmigration in mice exposed to cocaine, which was attenuated by pretreatment of mice with the sigma receptor antagonist. Interestingly, cocaine-mediated transmigratory effects were not observed in CCR2 knockout mice. We conclude that cocaine-mediated induction of MCP-1 accelerates monocyte extravasation across the endothelium. Understanding the regulation of MCP-1 expression and functional changes by cocaine/sigma receptor system may provide insights into the development of potential therapeutic targets for HIV-1-associated neurocognitive disorders.